1. Field of the Invention
The present invention relates to a bearing member including a cylindrical body rotatably supporting a shaft member and a method for manufacturing the bearing member, and to a dynamic pressure bearing device.
2. Description of Related Art
Bearing members that rotatably support a shaft member are widely used in various devices, but they are often made with copper metals such as phosphor bronze. Copper metals in general do not have good corrosion resistance and have a problem of being prone to discoloration and corrosion. In devices that require a clean environment, such as hard disk drive devices (HDD), anti-corrosion measures, e.g., plating, are rendered on the surface of the bearing member.
However, implementing anti-corrosion measures such as plating as discussed above requires a considerable amount of preparation and time, and the anti-corrosion measures are a cause behind lower productivity. Due to the fact that the plated film is a hard film, plating in particular makes subsequent processes difficult. Also, pieces and dusts of the plated film would likely adhere and/or remain in areas where the plated layer has been cut off, and the residue of hard pieces and dusts sometimes scratches or wears away the surface of a shaft member. Further, because the thickness of the plated layer can vary approximately xc2x120% and there are protrusions on the surface, a problem may occur in the precision of dimensions.
For example, in a dynamic pressure bearing device that utilizes the dynamic pressure of a lubricating fluid, because the dynamic pressure is generated in the lubricating fluid poured into a narrow bearing gap space, fluctuations in dimensions and protrusions can occur as described above when the plate layer is formed on the dynamic pressure surface and can have a great impact on the dynamic pressure performance.
It is an object of the present invention to provide a bearing member, its manufacturing method, and a dynamic pressure bearing device that can easily and effectively prevent discoloration and corrosion of the bearing member surface.
In order to achieve the above object, in a bearing member in accordance with one embodiment of the present invention and a dynamic pressure bearing device using the bearing member, a cylindrical body constituting a bearing member that rotatably supports a shaft member may be made of a copper metal, and an anti-rust film comprising cupric benzotriazole may be formed on the surface of the cylindrical body.
With such a bearing member, a favorable anti-rust effect can be obtained in a stable manner and a time-consuming anti-corrosion measures such as plating can be made unnecessary through the anti-rust film comprising cupric benzotriazole that can be formed easily. In addition, the anti-rust film comprising cupric benzotriazole forms extremely thinly and therefore causes virtually no fluctuations in the dimensions of the bearing member, and peeling problems can also be avoided due to the fact that the film has stable adhesion strength.
In the dynamic pressure bearing device according to the present invention, a lubricating fluid to which benzotriazole has been added may be used as a lubricating fluid inside a bearing gap space formed between the bearing member defining the cylindrical body and the shaft member. As a result, even if the anti-rust film comprising cupric benzotriazole formed on the surface of the bearing member is eliminated due to impact from heat, the benzotriazole added to the lubricating fluid would be supplied to the part of the anti-rust film that was eliminated and a new anti-rust film comprising cupric benzotriazole will be formed there.
Here, the benzotriazole added to the lubricating fluid may be between 0.01 wt. % and 10 wt. %.
Further in the dynamic pressure bearing device in accordance with the present invention, a capillary sealing section, which holds the lubricating fluid within the bearing gap space by surface tension, may be provided at the opening area of the bearing gap space.
When a capillary sealing section is provided at the opening area of the bearing gap, in the event the anti-rust film comprising cupric benzotriazole formed on the surface of the bearing member is eliminated due to impact from heat, the angle of contact of the lubricating fluid against the surface of the bearing member would become larger, causing the surface tension of the capillary sealing section to diminish, which would harm the sealing function of the lubricating fluid and increase the possibility of the lubricating fluid leaking to the outside. In contrast, in accordance with the present invention, the benzotriazole added to the lubricating fluid would be supplied anew to the part of the anti-rust film that was eliminated and form a new anti-rust film comprising cupric benzotriazole at the capillary sealing section. In other words, a new anti-rust film comprising cupric benzotriazole is automatically formed at the capillary sealing section when the anti-rust film comprising cupric benzotriazole formed on the surface of the bearing member is eliminated. The newly formed anti-rust film comprising cupric benzotriazole would cause the angle of contact of the lubricating fluid to be small again, and as a consequence the sealing function would be maintained well and the sealability of the lubricating fluid would be maintained favorably over a long period of time.
In the manufacturing method of a bearing member according to the present invention, a cylindrical body that supports a shaft member relatively rotatable with respect to the cylindrical body is formed with a copper metal and an anti-rust film comprising cupric benzotriazole may be formed on the surface of the cylindrical body. According to this manufacturing method, the anti-rust film comprising cupric benzotriazole can be easily formed and time-consuming anti-corrosion measures such as plating are rendered unnecessary.
In the manufacturing method in accordance with the present invention, the anti-rust film comprising cupric benzotriazole may be formed using a washing solution or a machining solution to which benzotriazole has been added.
In accordance with the present embodiment, the washing solution to which benzotriazole has been added may be a water-soluble washing solution used in a degreasing washing process following a finishing process of the cylindrical body. In addition, pure water to which a cleaning agent has been added may be used as the water-soluble washing solution, and the cleaning agent can have a surface-active agent as its primary component and have benzotriazole added to it. Further, the machining solution to which benzotriazole has been added may be a water-soluble cutting solution used in the cutting of the cylindrical body.
In accordance with the present invention, organic solvents used conventionally are unnecessary, and water stains and discoloration that are prone to occur in the drying process after washing with pure water can be favorably prevented by the anti-rust film comprising cupric benzotriazole formed on the surface of the bearing member.
Other features and advantages of the invention will be apparent from the following detailed description.